This invention relates to a novel approach for improving biophysical properties of antibodies, including a method for the stabilization of antibodies.
The biophysical stability of monoclonal antibodies is an important determinant of their usefulness and commercial value for several reasons (reviewed, among others, by Garber and Demarest, 2007, and by Honegger, 2008). First, high biophysical stability can result in high antibody expression yield in recombinant systems. High expression yield can facilitate antibody selection and screening, for example by enhancing the display level of antibodies on bacteriophages and by enhancing the soluble yield of antibodies in small-scale E. coli cultures, and therefore lead to the discovery of better antibody molecules. High expression yield can also be important in making the manufacturing of commercially available monoclonal antibodies economically viable by allowing a sufficiently small production scale suitable for the application. In monoclonal antibodies intended for therapeutic applications, high biophysical stability can be important as it can be associated with high solubility, therefore enabling antibodies to be efficiently formulated at high concentrations into drugs. Also in therapeutic monoclonal antibodies, high biophysical stability can be important for avoiding antibody aggregation during various manufacturing steps (including expression, purification, acid-mediated virus-deactivation and formulation) and during storage. The avoidance of aggregation is not only important to maximizing the economic viability of an antibody drug production process but is also thought to play an important role in minimizing the potential immunogenicity of antibody drugs in patients. Finally, also in therapeutic monoclonal antibodies, high biophysical stability is important in achieving a long antibody half-life both in patients and in disease models.
In recognition of the importance of high biophysical stability of monoclonal antibodies, researchers have aimed to improve the biophysical stability of monoclonal antibodies for the past several years. Research efforts have aimed to stabilize antibody constant domains, isolated antibody variable domains (especially autonomous VH domains known as VHH domains, VH domain antibodies, nanobodies or monobodies; but also autonomous VL domains), as well as heterodimeric antibodies comprising one VH and one VL domain. The read-out employed in such stabilization work has included increased expression yield, increased solubility of the expressed antibodies, increased levels of display in phage display libraries, increased resistance to denaturant-induced unfolding and increased resistance to heat-induced unfolding (known as thermal stability). In order to obtain antibody variable regions with improved biophysical stability, a variety of approaches has been taken that can be categorized as follows.
Researchers have employed specific antibody selection conditions, such as phage display with heat- or denaturant-induced stress during panning, to select antibody clones with superior biophysical properties, including reduced aggregation (Jung et al., 1999; Jespers et al., 2004(A); Dudgeon et al., 2008).
Researchers have employed specific antibody screening conditions, such as E. coli expression in the presence of reducing agents or fluorescent antigens able to permeate into the periplasm, or heating of secreted antibody clones in microtiter plates during antigen-specific ELISA screening, to select antibody clones with superior biophysical properties, including faster folding and greater thermal stability (Ribnicky et al., 2007; Martineau and Betton, 1999; Demarest et al., 2006).
Heterodimeric VH-VL antibody fragments have been stabilized by the addition of various entities such as chemical cross-linkers, peptide linkers to create single-chain Fv and single-chain Fab fragments, interchain disulphide bonds to create disulphide-stabilized Fv fragments, and heterodimeric coiled coils to create helix-stabilized Fv fragments (reviewed by Arndt et al., 2001).
Researchers have mutated framework residues at the VH-VL interface of heterodimeric VH-VL antibody fragments to obtain antibodies with greater resistance to denaturant-induced unfolding (Tan et al., 1998).
Heterodimeric VH-VL antibody fragments have been stabilized by increasing the hydrophilicity of solvent-exposed framework region residues. In some cases this has been done by disrupting hydrophobic patches at the antibody variable/constant domain interface (Nieba et al., 1997).
Autonomous VH domains have been stabilized by mutating positions otherwise contributing to the light chain interface, thereby improving solubility of this region that is buried in heterodimeric VH-VL antibodies (Davies and Riechmann, 1994; Riechmann, 1996; Bathelemy et al., 2007).
Autonomous VH domains have been stabilized by engineering additional intradomain disulphide bonds within the framework region (Davies and Riechmann, 1996) or between CDRs (Tanha et al., 2001).
In autonomous human and camelid VH domains, the CDR3 has been engineered to compensate for the hydrophobicity of the former light chain interface and to obtain better solubility of these domains (Tanha et al., 2001; Jespers et al., 2004(B); Dottorini et al., 2004).
In autonomous VL domains, a position in CDR1 (residue 32) and two positions in CDR2 (residues 50 and 56) have been engineered to increase the stability of the isolated VL domains towards denaturant-induced unfolding and to improve the feasibility of their potential use as disulphide-free intrabodies (Steipe, 1994; Ohage et al., 1997; Proba et al., 1998; Ohage and Steipe, 1999); all numbering according to Kabat (Kabat and Wu, 1991; Kabat et al., 1991).
Germline genes from which VH or VL antibody domains are derived have been identified and analysed, and their sequences compiled into databases (Lefranc et al., 1999; Retter et al., 2005), and family-specific key residues have been identified that are critical for the family-specific folding and side-chain-packing within the VH or within the VL domain (Ewert et al., 2003(A)). Then, by aligning germline genes, protein consensus sequences have been generated for variable domains that contain more of the family-specific key residues than variable domains derived from individual germline genes and as a result have potentially improved biophysical properties over variable domains derived from individual germline genes (Steipe et al., 1994; reviewed by Wörn and Plückthun, 2001). Resulting human variable domain consensus sequences have been used in the humanization of animal-derived monoclonal antibodies (for example, Carter et al., 1992) and in the construction of synthetic human antibody libraries (for example, Knappik et al., 2000).
11) Based on consensus sequences, human VH and VL germline families have been characterized, families with inferior or superior biophysical properties have been identified, and individual framework region residues responsible for the inferior or superior properties have been pin-pointed (for example, Ewert et al., 2003(A)). This has allowed researchers to generate antibodies with improved biophysical properties in several ways:
Human antibody clones of known specificity have been stabilized by human-to-human CDR grafting: Antigen-specific CDR loops and selected putative specificity-enhancing framework region residues from a donor clone derived from a human germline gene associated with inferior biophysical properties were transplanted onto a human acceptor framework associated with superior biophysical properties (Jung and Plückthun, 1997).
Human antibody clones of known specificity have been stabilized by framework-engineering: A set of framework region residues thought to be responsible for inferior properties of one germline family has been exchanged for a set of different framework region residues found in a germline family associated with superior properties, thereby improving the biophysical properties of the antibody clone while retaining most of the original framework region sequences and while retaining the specificity (Ewert et al., 2003(B)).
Based on the ranking of the biophysical properties of human germline family consensus genes in the context of VH-VL pairings, researchers have suggested that synthetic antibody libraries should be prepared in which only those germline families with a consensus that had shown superior biophysical properties in the VH-VL pairings (VH1, VH3 and VH5 as well as Vkappa1, Vkappa3 and Vlambda) should be represented (Ewert et al., 2003(A)).
Researchers have generated synthetic antibody libraries in which all germline families were represented, but all clones derived from a VH germline family associated with inferior biophysical properties (VH4) contained a point-mutation in the framework region designed to improve the biophysical properties of these clones (Rothe et al., 2008).
Researchers have generated synthetic libraries of VH-VL heterodimeric antibodies based on a single synthetic VH framework and a single synthetic VL framework (for example, Lee et al., 2004; Fellouse et al., 2007) or on a single synthetic VH framework and multiple synthetic VL frameworks (for example, Silacci et al., 2005) known for their favourable biophysical framework properties.
Efforts have been made to obtain naturally occurring and therefore potentially stable CDR conformations in synthetic libraries of single domain antibodies and VH-VL heterodimeric antibodies, in order to give the antibodies nature-like and good, albeit not especially improved, biophysical properties. To this end, some CDR positions that are known to be determinants of specific canonical CDR structures (Chothia et al., 1992; Tomlinson et al., 1995; Al-Lazikani et al., 1997) have been left undiversified or subjected to restricted diversification in many published synthetic antibody libraries, maintaining them as the dominant residue or residues most frequently found in the germline family context of the particular VH or VL domain on which the library is based. Among such positions that bear canonical-structure-determining CDR residues and that have been left undiversified or subjected to restricted diversification in published antibody libraries are positions 27, 29 and 34 in HCDR1, positions 52a, 54 and 55 in HCDR2, and positions 94 and 101 in HCDR3, as well as positions 90 and 95 in the LCDR3 of Vkappa domains (all numbering according to Kabat (Kabat and Wu, 1991)).
Also in efforts to obtain natural and potentially stable CDR conformations in synthetic libraries of single domain antibodies and VH-VL heterodimeric antibodies, other CDR residues buried within the VH domain or within the VL domain, which are naturally conserved independently of different specific canonical CDR structures, have been left undiversified or subjected to restricted diversification in some synthetic antibody libraries, maintaining them as the dominant amino acid most frequently found in nature (for example, VH position 51 in HCDR2 has been kept undiversified in several published synthetic human antibody libraries, bearing an invariant Ile).
However, despite that fact that many attempts have been made to provide stable antibodies and/or to stabilize existing antibodies, so far these attempts have had limited success.
Thus, there was still a large unmet need to provide novel methods for the stabilization of antibodies, including for the generation of antibody libraries. One important unmet need was that of stable human lambda antibodies exhibiting high thermal stability of the variable region but at the same time low levels of Fab constant region degradation during phage library production and during E. coli expression.
One application where Fab constant region degradation in human lambda antibodies has been particularly problematic is that of phage library production. Some ways of isolating antibody drug candidate molecules involve the generation of phage libraries that display antibody fragments, particularly Fab fragments on the surface of phage particles produced in E. coli, where the Fab fragment is expressed and incorporated or attached to the phage particle during phage assembly. This process requires that Fab fragments are displayed efficiently on the surface of the phage particle. The efficiency of display is usually dependent on intact Fab constant domains following expression in E. coli, because attachment to the phage particle is either mediated by a protein linker that forms an extension of one of the constant domains and is directly fused to a phage coat protein, or by a disulphide bond that is formed between a cysteine residue in the C-terminal region of one of the constant domains and a free cysteine residue engineered into one of the phage coat proteins. Incomplete expression, truncation or degradation (hereinafter simply referred to as degradation) of Fab constant regions during expression in E. coli would therefore result in inefficient display: In antibody clones where in the majority of molecules the constant regions are degraded during E. coli expression, only the minority can be displayed as intact Fab fragments, leading to inefficient phage library production. Importantly, if constant region degradation varies between library members, this leads to an under-representation of clones with more degraded constant regions in the displayed repertoire and therefore a lesser chance of isolating such clones as drug candidates.
Another application where Fab constant region degradation in human lambda antibodies has been particularly problematic is that of recombinant E. coli expression for antibody screening purposes. Some ways of isolating antibody drug candidates involve the screening of antibody clones as Fab fragments expressed in E. coli. In such screening campaigns, usually hundreds or thousands of antibody clones are expressed in individual wells of microtiter plates, and subjected to various analyses such as ELISA, SPR or biological assays. The read-out of these analyses is typically a signal that is correlated to the usefulness of the antibody clone, such as specificity or affinity. The intensity of the signal obtained in these analyses typically depends on antibody affinity and on the apparent concentration in which an antibody clone is present in the well of the microtiter plate. This concentration is commonly detected through secondary antibodies that bind to epitopes in the primary antibody's constant regions or to epitope tags fused to the primary antibody's constant regions. In both cases, detection depends on the presence and usually intact nature of the primary antibody's constant regions. If the constant regions are degraded during expression in E. coli, the concentration of the detected epitopes does not reflect the concentration at which the antibody was expressed and may not reflect the concentration of binding sites, formed by the variable regions that are present in the well of the microtiter plate. Again it is important to note that if constant region degradation varies between library members, this leads to a lower apparent concentration of clones with more degraded constant regions in the microtiter plate and therefore a lesser chance of isolating such clones as drug candidates.
The solution for this problem that has been provided by the present invention, i.e. the modification of particular residues in the constant region of lambda light chains, has so far not been achieved or suggested by the prior art.